Hi Rea,
For your question #1, it is certainly not required to pre-install your
software. I would even say that the only reason you should pre-install
your software is if you have very large software packages that only run
for a short time.
For small software packages (say less than a few MB, I am not sure what
the current limit is) you can send them with the input sandbox.
For larger software packages, you can register a tarball with the data
management system and have your jobs retrieve this tarball and install
it at run time.
We used the latter solution for D0. The tarball was about 700 MByte
large; picking it up and installing it took a few minutes. The few
minutes were a negligible overhead because the jobs ran for between
twelve and thirty hours.
Hope this helps.
JT
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